As is known to all, drivers of motor vehicles, racing bicycles and air vehicles all have to wear a helmet to protect the safety of their heads. There are two types of helmet here and now: including a full-face structure helmet and a half-face structure helmet, wherein the full-face structure helmet is provided with a jaw protector surrounding a jaw of a driver while the half-face structure helmet is not provided with such jaw protector; and the full-face helmet may protect the user preferably due to the jaw protector, while the half-face helmet is more conveniently worn due to an opened structure. A typical full-face helmet generally comprises a helmet housing body, a protective guard, a jaw protector and other members, wherein both the protective guard and the jaw protector are installed on the helmet housing body, the protective guard may be opened or buckled according to the need, playing a role in preventing such harmful particles as dust, rainwater and the like as well as raindrop from invading into the helmet to ensure the driver can also drive regularly in poor working conditions, while the jaw protector may effectively protect such vital organs as jaw, mouth, nose and the like of the driver while an accident collision happens. The jaw protector and the helmet housing body of a traditional full-face helmet are in a manufacturing mode of an integral structure, that is to say, the jaw protector is fixed relative to the helmet housing body. Without question, such integral structure of the traditional full-face helmet is firmer, so that it has enough safety; however, the full-face helmet in the integral structure also has defects of inconvenience in use and difficulty in production and manufacture, and the like. On one hand, from a use point of view, when the driver needs to drink water, communicate by phone and take other actions and so on, he has to remove the helmet to complete corresponding actions; at this time, the traditional full-face helmet seems to be very slack and inconvenient; while on the other hand, from a production and manufacture point of view, a production mould for the integrated full-face helmet seems to be very complicated due to a jaw protecting structure, so that its manufacturing cost is very expensive. Obviously, the traditional full-face helmet in the integral structure fails to meet multi-purpose requirements of safety, convenience, low cost and so on. In view of this, Spain patent application ES2329494T3 discloses a helmet with a transformable jaw protecting structure; in addition, China invention patent ZL201010538198.0 also proposes a helmet with a transformable jaw protecting structure capable of mutually transforming a full-face helmet structure and a half-face helmet structure. The two helmets with the transformable jaw protecting structure have common features as follows: firstly, the jaw protector and the helmet housing body adopt a separate structure so that the production and manufacture cost of the helmet may be reduced; secondly, the jaw protector can open and climb over the protective guard even in an opening position from the full-face helmet structure position according to the need to become a half-face helmet, the function is obtained using a slit-like rail slot in a mount and a jaw protector prong and a constraint pin in a movement coordination with the slit-like slot to dynamically control a position and posture of the jaw protector, in other words, a change in the jaw protecting structure totally depends on the rail slot with a through character to constrain. There is no doubt that a scheme that the above two helmets adopt the transformable jaw protecting structure meets the multi-purpose requirements of convenience and low cost preferably, thereby advancing helmet technologies.
However, although the advantages of the above-mentioned two helmets with the transformable jaw protecting structure are readily understood, their disadvantages are also extremely highlighted due to a structure scheme of the slit-like rail slot adopted, with specific performance as follows: 1) the existence of the rail slot with a through character is likely to result in deteriorating the safety of the helmet, for instance, the helmet with the transformable jaw protecting structure disclosed by the Spain patent application ES2329494T3 is provided with a plurality of flat constraint rail slots in its mount and chin of jaw protector, while China patent ZL201010538198.0 is also provided with a similar flat rail slot in its mount, it is obvious that excessive rail slot slit-like structures will inevitably damage the structural intensity and rigidity of corresponding members. This is because that on one hand, it will inevitably damage the integrality of the structural layout, and on the other hand, it will bring concentration of stress. It has to be noted that the scheme of the rail slot will weaken the intensity and rigidity of these important members, so that the safety of the helmet is dramatically reduced; 2) the existence of the rail slot with the through character will inevitably reduce the amenity of the helmet. As is known to all, a powerful relative air current will be produced inevitably in a process that the driver wearing the helmet drives the motor vehicle to run. Since there are multiple slit-like rail slots, the helmet fails to be covered completely and most is in an exposed state. When the air current blowing the helmet flows through surfaces of these rail slots, high air current buzzing noises will be made, and the faster a running speed the higher the noise intensity derived. It is noted that the rail slot is arranged near ears of the driver, so that it will inevitably have a strong impact on the driving comfort of the driver; in addition, the opened rail slot still fails to prevent the rainwater from invading, this not only seriously impacts on a mood of the driver but also seriously interferes with the driving safety of the driver when driving in rainy days, not to mention an increase in driving enjoyment, so that the experience feeling is poor. It is visible that the current helmet with the transformable jaw protector having the rail slot character will result in seriously reducing the amenity; 3) The existence of the rail slot with the through character will inevitably reduce the reliability of the helmet. On one hand, as previously mentioned, the slit-like rail slot will seriously weaken the rigidity and intensity of these important members including the jaw protector and the mount, so that the reliability of the helmet product is reduced; on the other hand, the slit-like rail slot will also increase the assembly complicacy of the helmet, so that the difficulty in assembly is dramatically increased. This is because that a separate impact of the rail slot not only increases a number of parts, but also dramatically increases the complexity of its assembly procedure to make regulation more difficult; in the meanwhile, a constraint pair formed by the slit-like rail slot and a moving pin belongs to an imprecise kinematic pair, a fit clearance of which is difficult to control and easily causes a decrease in the movement stability of the jaw protector very much. It is thus clear that the decrease in the intensity and rigidity of the parts and the increase of the number and assembly difficulty, or the consistency of the fit clearance between the rail slot and the moving pin are difficult to ensure. As a final result, the quality reliability of the helmet is reduced.
In conclusion, using the helmet with the transformable jaw protecting structure based on rail slot constraint in the prior art can achieve the structure transfer of the jaw protector between the full-face helmet position and the half-face helmet position, but has more hidden dangers and disadvantages in terms of safety, comfort, reliability and the like as well. Therefore, it is still necessary to further improve and prompt the helmet.